4790 is the way to go if you have the money for it, but an SSD is going to be a more immediate difference for half the price.

The easiest way to transfer is to reduce your windows partition small enough that it would fit into the SSD and use a program like CloneZilla to clone the drive. Or if you don't care about reinstalling your programs then you can just unplug the other hard drives, install windows on the SSD and use your other drive as a secondary drive.